Sensing pressure is useful for a variety of medical purposes. For example, treatment of hydrocephalus can involve monitoring the pressure of cerebrospinal fluid (CSF). Hydrocephalus is a neurological condition that is caused by the abnormal accumulation of CSF within the ventricles, or cavities, of the brain. CSF is a clear, colorless fluid that is primarily produced by the choroid plexus and surrounds the brain and spinal cord. CSF constantly circulates through the ventricular system of the brain and is ultimately absorbed into the bloodstream. CSF aids in the protection of the brain and spinal cord. Because CSF keeps the brain and spinal cord buoyant, it acts as a protective cushion or “shock absorber” to prevent injuries to the central nervous system.
Hydrocephalus, which affects children and adults, arises when the normal drainage of CSF in the brain is blocked in some way. Such blockage can be caused by a number of factors, including, for example, genetic predisposition, intra-ventricular or intra-cranial hemorrhage, infections such as meningitis, head trauma, or the like. Blockage of the flow of CSF consequently creates an imbalance between the amount of CSF produced by the choroid plexus and the rate at which CSF is absorbed into the bloodstream, thereby increasing pressure on the brain, which causes the ventricles to enlarge.
Hydrocephalus is most often treated by surgically inserting a shunt system that diverts the flow of CSF from the ventricle to another area of the body where the CSF can be absorbed as part of the circulatory system. Shunt systems come in a variety of models and typically share similar functional components. These components include a ventricular catheter which is introduced through a burr hole in the skull and implanted in the patient's ventricle, a drainage catheter that carries the CSF to its ultimate drainage site, and optionally a flow-control mechanism, e.g., shunt valve, that regulates the one-way flow of CSF from the ventricle to the drainage site to maintain normal pressure within the ventricles. The pressure within the shunt valve, which can resemble the intra-ventricular pressure, may need to be measured and the results non-invasively communicated to a remote device.
Current pressure sensors are often large, particularly relative to the size of a shunt valve, involve complex circuitry for measurement or communication, and consume an inordinate amount of power. Accordingly, there remains a need for a pressure sensor effective to measure pressure within a body or within an implanted medical device, such as a implanted hydrocephalus shunt valve.